Buggy code:
class StyledTextRenderer { Device device ; StyledText styledText ; StyledTextContent content ; Font regularFont ; Font boldFont ; Font italicFont ; Font boldItalicFont ; int tabWidth ; int ascent ; int descent ; int averageCharWidth ; int topIndex = - 1 ; TextLayout [ ] layouts ; int lineCount ; int [ ] lineWidth ; int [ ] lineHeight ; StyledTextRenderer . LineInfo [ ] lines ; int maxWidth ; int maxWidthLineIndex ; boolean idleRunning ; Bullet [ ] bullets ; int [ ] bulletsIndices ; int [ ] redrawLines ; int [ ] ranges ; int styleCount ; StyleRange [ ] styles ; StyleRange [ ] stylesSet ; int stylesSetCount = 0 ; boolean hasLinks ; boolean fixedPitch ; static final int BULLET_MARGIN = 8 ; static final boolean COMPACT_STYLES = true ; static final boolean MERGE_STYLES = true ; static final int GROW = 32 ; static final int IDLE_TIME = 50 ; static final int CACHE_SIZE = 128 ; static final int BACKGROUND = 1 << 0 ; static final int ALIGNMENT = 1 << 1 ; static final int INDENT = 1 << 2 ; static final int JUSTIFY = 1 << 3 ; static final int SEGMENTS = 1 << 5 ; static class LineInfo { int flags ; Color background ; int alignment ; int indent ; boolean justify ; int [ ] segments ; public LineInfo ( ) { } public LineInfo ( StyledTextRenderer . LineInfo info ) { } } StyledTextRenderer ( Device device , StyledText styledText ) { } int addMerge ( int [ ] mergeRanges , StyleRange [ ] mergeStyles , int mergeCount , int modifyStart , int modifyEnd ) { } int addMerge ( StyleRange [ ] mergeStyles , int mergeCount , int modifyStart , int modifyEnd ) { } void calculate ( int startLine , int lineCount ) { } void calculateClientArea ( ) { } void calculateIdle ( ) { } void clearLineBackground ( int startLine , int count ) { } void clearLineStyle ( int startLine , int count ) { } void copyInto ( StyledTextRenderer renderer ) { } void dispose ( ) { } void disposeTextLayout ( TextLayout layout ) { } void drawBullet ( Bullet bullet , GC gc , int paintX , int paintY , int index , int lineAscent , int lineDescent ) { } int drawLine ( int lineIndex , int paintX , int paintY , GC gc , Color widgetBackground , Color widgetForeground ) { } int getBaseline ( ) { } Font getFont ( int style ) { } FontData [ ] getFontData ( int style ) { } int getHeight ( ) { int defaultLineHeight = getLineHeight ( ) ; if ( styledText . isFixedLineHeight ( ) ) { <START_BUG> return ( lineCount ) * defaultLineHeight ; <END_BUG> } int totalHeight = 0 ; int width = styledText . getWrapWidth ( ) ; for ( int i = 0 ; i < ( lineCount ) ; i ++ ) { int height = lineHeight [ i ] ; if ( height == ( - 1 ) ) { if ( width > 0 ) { int length = content . getLine ( i ) . length ( ) ; height = ( ( ( length * ( averageCharWidth ) ) // width ) + 1 ) * defaultLineHeight ; } else { height = defaultLineHeight ; } } totalHeight += height ; } return ( totalHeight + ( styledText . topMargin ) ) + ( styledText . bottomMargin ) ; } boolean hasLink ( int offset ) { } int getLineAlignment ( int index , int defaultAlignment ) { } Color getLineBackground ( int index , Color defaultBackground ) { } Bullet getLineBullet ( int index , Bullet defaultBullet ) { } int getLineHeight ( ) { } int getLineHeight ( int lineIndex ) { } int getLineIndent ( int index , int defaultIndent ) { } boolean getLineJustify ( int index , boolean defaultJustify ) { } int [ ] getLineSegments ( int index , int [ ] defaultSegments ) { } int getRangeIndex ( int offset , int low , int high ) { } int [ ] getRanges ( int start , int length ) { } StyleRange [ ] getStyleRanges ( int start , int length , boolean includeRanges ) { } StyleRange getStyleRange ( StyleRange style ) { } TextLayout getTextLayout ( int lineIndex ) { } TextLayout getTextLayout ( int lineIndex , int orientation , int width , int lineSpacing ) { } int getWidth ( ) { } void reset ( ) { } void reset ( int startLine , int lineCount ) { } void setContent ( StyledTextContent content ) { } void setFont ( Font font , int tabs ) { } void setLineAlignment ( int startLine , int count , int alignment ) { } void setLineBackground ( int startLine , int count , Color background ) { } void setLineBullet ( int startLine , int count , Bullet bullet ) { } void setLineIndent ( int startLine , int count , int indent ) { } void setLineJustify ( int startLine , int count , boolean justify ) { } void setLineSegments ( int startLine , int count , int [ ] segments ) { } void setStyleRanges ( int [ ] newRanges , StyleRange [ ] newStyles ) { } void textChanging ( TextChangingEvent event ) { } void updateBullets ( int startLine , int replaceLineCount , int newLineCount , boolean update ) { } void updateRanges ( int start , int replaceCharCount , int newCharCount ) { } }

Fix:
return ( ( ( lineCount ) * defaultLineHeight ) + ( styledText . topMargin ) ) + ( styledText . bottomMargin ) ;